Manufacture of fluorine containing polymers



Dec. 18, 1956 H. J. PASSING ET AL Filed June 11. 1953 FIG.|

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HERBERT J. PASSING JOHN M. WRIGHTSON ALBERT L. DITTMAN Ill flak ATTORN EYS United States Patent MANUFACTURE OF FLUORINE CONTAINING POLYMERS Herbert J. Passino, Englewood, and Albert L. Dittman, North Bergen, N. J and John M. Wrightson, Whittier, Calif., assignors to The M. W. Kellogg Company, Jersey City, N. 1., a corporation of Delaware Application June 11, 1953, Serial No. 360,893 12 Claims. (Cl. 260-875) This invention relates to a method of manufacturing fluorinated plastics. In one of its aspects, this invention relates to a method for polymerizing fiuorochloroolefins to produce a normally solid polymer. in another of its aspects, this invention relates to the polymerization of perfluorochloroolefins in an aqueous-suspension medium to produce a normally solid polymer. In one of its more particular aspects, this invention relates to the polymerization of trifluorochloroethylene in a pesulfate, bisulfite promoted aqueous system accelerated with iodide ion to produce a normally solid thermoplastic polymer.

The present invention is a continuation-in-part of our prior and copending application Serial No. 213,524, filed March 2, 1951, now U. S. Patent No. 2,689,244, which application discloses polymerization of halogenated olefins in aqueous systems.

The polymerization of fluorochloroolefins results in the production of a variety of useful materials. For example, the polymerization of trifiuorochloroethylene under conditions suitable for the production of the solid polymer yields a material of extraordinary chemical resistance and desirable physical characteristics. The chemical resistance of polytrifluorochloroethylene is such that it will withstand exposure to a wide variety of oxidizing, reducing and solvent type materials such as fuming nitric acid, hydrazine, acetone, aniline, etc. Physically, the material possesses higher thermal stability, tensile strength, etc. In addition to the above properties, these polymers are readily molded into various useful articles such as valves, gaskets, diaphragms, etc., using conventional equipment with operating conditions adjusted in accordance with the characteristics of the polymer.

The present method for producing solid polytrifluorochloroethylene is by a bomb or mass-bulk type reaction at relatively low temperatures. The polymerization is effected, under suitable polymerization conditions, with or without the presence of a suitable catalyst or promoter. Such conditions comprise the use of a suitable catalyst, such as bis-trichloroacetyl peroxide dissolved in a suitable solvent, such as trichlorofiuorornethane, at a temperature between about 20 and about 50 C. After a period of about 7 days the bomb is opened and a porous-plug of polymer containing monomer within the interstices of the plug is removed. The monomer is evaporated and the plug is broken into chips or granules for further processing.

It is an object of this invention to provide a process ICC for polymerizing fiuorochloroolefins, to produce polymer in relatively high yields.

Another object of this invention is to provide a process in which polymerization of fiuorochloroolefins may be effected in relatively short periods of time and with good yields from an economic standpoint.

Another object of this invention is to provide an accelerator for increasing yields of polymer and decreas ing the time of polymerization.

it is one of the more particular objects of this invention to provide a process for producing normally solid thcrmo plastic polymers of tritiuorochloroethylene having a no strength temperature above about 220 C. in high yields.

Various other objects and advantages of the present invention will become apparent to those skilled in the art from the accompanying description and disclosure.

As herein defined, polymerization refers to the polymerization of a single monomer and also to the copolymerization ot unlike monomers to produce polymers and copolymers.

According to this invention, a substituted ethylene con taining at least two fluorine atoms, preferably at least one fluorine atom per carbon atom of the aliphatic portion of the substituted ethylene, is polymerized in the presence of an aqueous-suspension medium under suitable conditions of temperature, pressure, residence time and promoting agent to produce a normally solid, thermoplastic polymer. The polymerization process of this invention may be affected in either a batchwise or continuous manner. The monomer is admixed with the aqueous-suspension medium in a suitable polymerization zone which is maintained at the appropriate conditions of polymerization and under sufficient pressure to maintain the aqueous solution as a liquid under the conditions of polymerization. The monomer and water are agitated by suitable means in the reaction zone so as to intimately disperse the monomer and aqueous-suspension medium. The monomer and polymer are substantially insoluble in the aqueous dispersion medium. The separation of the polymer from the Water phase may be effected by settling and decantetion, by filtering, by centrifuging, by evaporation, or by various other conventional methods.

The present invention is particularly applicable to the polymerization of perfluoroehloroolefins, such as tritluorochloroethylene. However, the invention contemplates the polymerization of various halogenated olefins. For example, perfluorobutadiene, perfiuoropropcne, phenyL trifiuoroethylenc, alpha methyl. phenyl diiiucroethylcne, perfiuoro acrylonitrile. perfluorostyrene, perfluorocyelobutene, perfluorocyclobutadiene, tetrafiuoroethylene, vinylidine fluoride, trifiuoroethylene and difluorodichloroethylene. As previously mentioned, the invention applies to the copolymerization of these monomers, as well as their homopolymerization. For example, the invention applies to the copolytnerization of trifiuorochloroethylene and tetrafluoroethylene, of trifluoroehloroethylene and vinylidene fluoride, triiluorochloroethylene and vinyl fluoride, trifiuorochloroethylene and vinyl chloride, trifiuorochloroethylene and vinylidene chloride, trifluorochloroethylene and perfluoropropene, trifluorochloroethylene and trifluoroethylene, and of periluorobutadiene and perfluorostyrene. In these copolymerizations, the second monomer is also preferably a fiuorinated olefin and prefernbly contains at least two fluorine atoms per molecule. When less than 5 weight percent comonomer is employed, the polymerization is broadly included within the term homopolymerization.

The quantity of water employed as the aqueous-sus pension medium is usually between about 0.05 to about times by volume of the quantity of total monomer present in the reaction zone. Preferably, the quantity of water is between one and five times the total monomer in the reaction zone.

The temperature employed for the polymerization will depend to a certain extent upon the particular monomer being polymerized. While the temperature may be varied depending upon the type of monomer, it is preferred that the temperature be maintained below about 40 C. Temperatures above 40 C. result in the production of nonthermoplastic polymers, i. e. Waxes and oils. depending on the extent to which the temperature has been raised above 40 C. As the temperature is decreased the reaction time increases. Temperatures below about 0 C. cannot be used. Therefore, this invention contemplates the use of temperature above about 0 C. and below about 40 C. In the polymerization of trifiuorochloroethylene, temperatures between about 10 C. and about 30 C. are preferred. Still more preferable, are temperatures betwen about C. and about C. while a particularly suitable temperature is about 20 C. for the production of high N. S. T. polymers of trifiuorochloroethylene i. e. polymers having an N. S. T. of above about 320 C.

The time of polymerization also depends upon the monomer being polymerized, but in general, times between about 10 minutes and about 72 hours may be employed. A preferred polymerization time is between about 20 and about 50 hours. Generally, the polymerization time will not exceed 96 hours.

The aqueous phase type of polymerization for the above monomers usually requires a suitable promoting agent to effect the polymerization in a reasonable length of time and to produce a polymer of the desired molecular weight. These promoting agents fall in three general classes; promoters, activators and accelerators. ln almost all instances, a promoter must be used. Such promoters comprise the inorganic peroxides. Examples of suitable inorganic peroxides are the water-soluble peroxides. such as the perborates, persulfates, perphosphates, percarbonates. barium peroxide, zinc peroxide, and hydrogen peroxide. Particularly valuable are the watersoluble salts of the peracids, such as sodium, potassium. calcium. barium and ammonium salts of persulfuric and perphosphoric acids which may be prepared in the conventional manner by electrolytic oxidation of salts of the corresponding oxy acids. Suitable concentration of the promoter lies within the range of 0.003 molar to about 0.1 molar. The exact quantity of promoter will depend upon the monomer, molecular weight of the polymer desired and the particular promoter being employed. For example. in the polymerization of trifiuorochloroethylene to produce the solid polymer thereof having an N. S. T. above 220 C. a promoter concentration between about 0.003 and about 0.07 molar, or about 0.01 and about 2.0 percent by weight based on water, is preferred. Generally, the concentration is not higher than about 0.09 molar.

Promoters are also preferably used in conjuction with an activator. Such activators comprise sodium bisulfite, sodium hydrosulfite, sodium thiosulfate and trimethylamine, and in general any water-soluble reducing agent. These activators are generally employed in concentrations similar to the concentration of promoter employed.

Equimolar amounts of promoter and activator are preferred.

Buffering agents may be employed also to obtain optimum pH conditions. For example, when an alkaline pH is desired, buffers such as borax, disodium phosphate, sodium carbonate, ammonium carbonate, and sodium acetate may be used. For an acid pH, acetic acid, propionic acid and monosodium phosphate may be employed. It is preferred to maintain a pH between about 1 and about 4.

It has been found that high yields of polymer may be obtained in relatively short periods of time by the use of water-soluble iodine compounds. These water-soluble iodine compounds, or accelerators, ionize in water to pro duce iodide ion. The accelerator in its oxidized state is more readily reducible than the promoter and in its reduced state is more readily oxidizable than the activator. Various water-soluble salts of iodine may be employed, such as for example potassium iodide, sodium iodide, calcium iodide, lithium iodide, strontium iodide, etc. A particularly suitable iodine compound is potassium iodide. The iodine compound is dissolved in the aqueous reaction mixture and is present in an amount between about 1 and about 1000 p. p. m. The quantities of iodine accelerator compound are given in p. p. m. of iodine unless otherwise indicated. In the polymerization of trifiuorochloroethylene, it is preferred to use between about 3 and about 400 p. p. m. of iodine compound accelerator. At relatively low temperatures between about and about 400 p. p. in. may be used, while at higher temperatures the concentration of accelerator is preferably kept between about 3 and about 150 p. p. in. since high temperatures combined with high iodide ion concentration tend to produce brittle polymers, i. e. oils and waxes. The copolymerization of trifluorochloroethylene with other fluorinated olefinic monomers and the polymerization of monomers other than trifluorochloroethylene may require accelerator concentrations as high as 1000 p. p. In.

It is preferred to maintain the water phase substantially free from water-soluble organic compounds, such as alcohols and ketones, since such compounds are inhibitors for the polymerization of trifiuorochloroethylene and have a marked adverse effect on the polymerization reaction and on the characteristics of the product produced. The use of purified or distilled water is thus preferred.

In carrying out the process of this invention using an accelerator, the polymerization is effected in a vessel or conduit which is not capable of being attacked by the ingredients employed in the polymirization. Suitable corrosive resistant materials useful for construction or lining of the reaction vessel or conduit comprise stainless steel, inconel, Monel, silver, nickel, glass or fluorinated solid polymers. In all cases, the liquid in the reaction zone must be vigorously agitated to maintain the reactant and promoting agents in intimate contact. The vigorous agitation of the liquid phase of the reactor may be obtained by high speed stirring, such as with small propellers connected by means of a shaft to a high speed electric motor. Forced circulation of the liquid phase through orifices or small diameter conduits is also an effective method for achieving intimate mixing of the reactant, water and promoting agents. In general, any system suitable for obtaining a mechanical emulsion without using detergents will be applicable since, in most instances, detergents are harmful to the polymerization reaction.

It is within the scope of this invention to disperse finelydivided solids in the liquid phase as a suspension for the purpose of forming nuclei for the start of the polymerization. The following are examples of such fillers: various pigments such as titanium dioxide, carbon black, clays, asbestos, glass fiber, and other relatively inert solids.

A series of polymerization runs were made in order to more clearly show the etfect on the yield and the no strength temperature of polymer resulting from variation in temperature and accelerator concentration. These data are presented in the table below. All runs were made using a 16.2 to 1 mol ratio of water to monomer. Equimolar concentration of potassium persulfate and TABLE Tabulated data ing a substituted ethylene compound having at least 2 fluorine atoms in the molecule at a temperature above about C. and below 40 C. in the presence of an aqueous-suspension medium having a water-soluble inorganic peroxide as a polymerization promoter, a water- Temp., Time, Percent Percent N. S. T., Percent P. in Run No. 0. hr. yield day O. KaSaOu I remaining 96 13. 6 3. 4 248 60. 8 50 72 22. 3 7. 4 320 5B. 2 50 46 9. 45 4. 93 70. 2 l 20 46 12. 95 6. 75 293 64. 8 5 2D 40 17. 10 8. 92 292 58. 1 50 20 46 18. 16 9. 47 258 41. 8 500 20 46 12. 0 6. 26 25. 7 1, 000 20 46 33. 3 17. 4 275 27. 0 500 48 20. 7 10. 4 292 60. 8 50 30 48 37. 6 18. S 260 56. 8 50 43 61. 4 34. 3 246 62. 2 50 29-38. 5 l6 5 36. 4 52. 7 247 66. 2 50 sodium bisulfite were used. 0.074 of the concentration were employed in all cases except run No. 8, which is indicated by an asterisk, where a 0.0185 molar concentration was employed. Accelerator concentration is given in parts per million of potassium iodide; the corresponding concentration in terms of iodine may be readily calculated.

Figures 1, 2, and 3 of the drawings are presented to show the effect of potassium iodide accelerator concentration. Specifically, Figure l of the drawing presents a comparison between the yield of polymer, obtained at various temperatures using a 50 p. p. m. concentration of potassium iodide, and an equivalent but nonaccelerated system i. e. a system which did not employ potassium iodide. Figure 2 of the drawing illustrates the effect of temperature on the N. S. T. of the polymer produced in a system which was accelerated with 50 p. p. m. of potassium iodide. Figure 3 of the drawing illustrates the effect, on yield of polymer, of varying concentrations of potassium iodide. Examination of the figures of the drawing leads to the following conclusions. The use of a potassium iodide accelerator more than doubles the yield of polymer produced. The higher the N. S. T. of the polymer desired the lower must be the temperature employed at a given accelerator concentration. For example, a temperature of about 20 C. is preferred for the production of polymer having an N. S. T. of above about 320 C. in a system accelerated with about 50 p. p. m. of potassium iodide, i. e. approximately p. p. m. as iodine. The efiect of potassium iodide concentration on the yield of polymer produced at a polymerization temperature of about 20 C. is very pronounced at concentrations up to about 100 p. p. m. at which point the curve levels oil and no significant increase is observed. The optimum concentration in terms of potassium iodide is therefore, about 100 p. p. m. with a particularly suitable concentration of about p. p. m. at about 20 C.

The data presented in the figures of the drawings are based on observations made with respect to the homopolymerization of trifluorochloroethylene but, as will be evident to those skilled in the art, are applicable to other polymerization systems. It is, of course, obvious, that the concentration of accelerator will vary depending on the monomer being polymerized and, also, on the molar concentration of promoter and activator used.

Various modifications and alterations of the procedures of this invention which will be obvious to those skilled in the art may be made without departing from the scope of this invention.

Having thus described our invention we claim:

1. A process for the production of a normally solid fluorine-containing polymer which comprises polymerizsoluble reducing agent as an activator, selected from the 25 group consisting of alkali bisulfites, alkali hydrosulfites. alkali thiosulfates and trimethylamine and an amount of a water-soluble iodide as an accelerator within a range between about 1 and 1000 p. p. m. calculated as iodine.

2. The process of claim 1 in which the substituted 30 ethylene compound is trifluorochloroethylene.

between about 24 and about 72 hours in an aqueous-sus- 3. The process of claim 1 in which the substituted ethylene is difluorodichloroethylene.

4. The process of claim 1 in which the substituted ethylene compound is tritiuorochloroethylene and is copolymerized with vinylidene fluoride.

5. The process of claim 1 in which the substituted ethylene compound is trifluorochloroethylene and is copolymerized with tetrafluoroethylene.

m 6. The process of claim l in which the substituted ethylene compound is trifiuorochloroethylene and is copolymerized with trifiuoroethylene.

7. A process for the production of a thermoplastic polymer of trifluorochloroethylene which comprises polymerizing tritluorochloroethylene in a polymerize tion zone at a temperature above about 0 C. and below 40 C. in the presence of an aqueous-suspension medium containing an alkali persulfate as a promoter and an alkali bisulfite as an activator and a water-soluble iodide as an accelerator said water-soluble iodide being present in an amount between about 3 and about 400 p. p. m. calculated as iodine.

8. A process for the production of a thermoplastic polymer of trifluorochloroethylene having an N. S. T. above about 220 C. which comprises polymerizing trifluorochloroethylene in a polymerization zone at a temperature above about 0 C. and below 40 C. in the presence of an aqueous-suspension medium containing at least about 0.003 molar concentration of potassium persulfate as a promoter and sodium bisulfite as an activator and between about 3 and about 400 p. p. m. or potassium iodide calculated as iodine.

9. A process for the production of a thermoplastic polymer of trifluorochloroethylene having an N. S. T. above about 220 C. which comprises h0mo-polymeriz ing trifiuorochloroethylene in a polymerization zone at a temperature between about 10 C. and about 30 C. for a period of time between about 24 and about 72 hours in an aqueous-suspension medium containing approximately equimolar quantities of potassium persulfate as a promoter and sodium bisulfite as an activatorand between about 3 and about 400 p. p. m. of potassium iodide calculated as iodine.

10. A process for the production of a thermoplastic 75 polymer of trifiuorochloroethylene which comprises polymerizing trifluorochloroethylene in a polymerization zone whose contact area consists of a substantially corrosion-re sistant material at a temperature above about 0 C. and below 40 C. for a period of time between about 24 hours and about 72 hours in an aqueous-suspension medium containing at least 0.003 molar concentration of potassium perborate as a promoter and sodium thiosulfate as an activator and between about 3 and about 400 p. p. m. of potassium iodide calculated as iodine and maintaining the pH of the aqueous-suspension medium between about 1 and about 4.

ll. A process for the production of a thermoplastic polymer of trifluorochloroethylene which comprises polymerizing trifiuorochloroethylene in a polymerization zone whose contact area consists of glass, at a temperature between above about 0 C. and below 40 C. for a period of time between about 24 and about 72 hours in an aqueous-suspension medium containing approximately equimolar quantities of barium peroxide as a promoter and sodium hydrosulfate as an activator and between about 3 and about 400 p. p. m. of sodium iodide calculated as iodine and maintaining the quantity of Water between 0 about 0.05 and about 10 times by volume the volume of monomer.

12. A process for the production of a thermoplastic polymer of tritiuorochloroethylene having an N. S. T. above about 220 C. which comprises homo-polymerizing trifiuorochloroethylene in a polymerization zone whose contact area consists of stainless steel at a temperature above about 0 C. and below 40 C. for a period of time pension medium containing at least 0.003 molar concentration of hydrogen peroxide as a promoter and of trimethylamine as an activator in approximately equimolar quantities and between about 3 and about 400 p. p. m. of calcium iodide calculated as iodine and maintaining the pH of the aqueous-suspension medium between about 1 and about 4, and the quantity of the aqueous-suspension medium between about 0.05 and about 10 times by volume the volume of monomer.

References Cited in the file of this patent UNITED STATES PATENTS 2,569,524 Hamilton Oct. 2, 1951 

1. A PROCESS FOR THE PRODUCTION OF A NORMALLY SOLID FLUORINE-CONTAINING POLYMER WHICH COMPRISES POLYMERIZING A SUBSTITUTED ETHYLENE COMPOUND HAVING AT LEAST 2 FLUORINE ATOMS IN THE MOLECULE AT A TEMPERATURE ABOVE ABOUT 0* C. AND BELOW 40* C. IN THE PRESENCE OF AN AQUEOUS-SUSPENSION MEDIUM HAVING A WATER-SOLUBLE INORGANIC PEROXIDE AS A POLYMERIZATION PROMOTER, A WATERSOLUBLE REDUCING AGENT AS AN ACTIVATOR, SELECTED FROM THE GROUP CONSISTING OF ALKALI BISULFITES, ALKALI HYDROSULFITES, ALKALI THIOSULFATES AND TRIMETHYLAMINE AND AN AMOUNT OF A WATER-SOLUBLE IODIDE AS AN ACCELERATOR WITHIN A RANGE BETWEEN ABOUT 1 AND 1000 P.P.M. CALCULATED AS IODINE. 